This invention relates to fluid control apparatus, and more particularly to devices that employ microminiature valves, sensors and other components for controlling pressure responsive valves in fluid passages.
Fluid valves typically employ flexible membranes or other pressure responsive elements in governing fluid flow. A typical valve includes a housing with inlet and outlet ports, and a valve seat along the main passage between the ports. A flexible membrane or diaphragm near the valve seat forms a partition between the passage and a pressure chamber. An intake passage to the pressure chamber communicates with the inlet port, whereby fluid can enter the chamber. An outlet passage from the chamber to the outlet port provides pressure relief. An electromagnetic servo valve or pilot valve is provided in the outlet passage.
When the pilot valve is closed, fluid enters the pressure chamber via the intake passage and increases pressure in the chamber, flexing the diaphragm against the valve seat to prevent fluid flow through the main passage. Opening of the servo valve permits fluid flow out of the chamber through the outlet passage, and the diaphragm is removed from the valve seat in response to the diminishing fluid pressure in the pressure chamber, thus opening the main valve. An exemplary valve of this type is a hydraulic valve disclosed in U.S. Pat. No. 4,418,886 (Holzer).
U.S. Pat. No. 4,898,200 (Odajima et al) and U.S. Pat. No. 4,722,360 (Odajima et al) disclose fluid control devices in which a nozzle back pressure is selectively varied to control a valve positioned between a supply port and an output port. The control mechanism includes side-by-side piezoelectric ceramic members movable between open nozzle and closed nozzle positions. When the nozzle is open, back pressure, atmospheric pressure and supply pressure reach an equilibrium that keeps the main valve closed.
U.S. Pat. No. 3,414,010 (Sparrow) discloses a modulating valve in which current to an electromagnet flexes a magnetostrictive bimetal member, in turn flexing a modulating valve diaphragm to restrict fluid flow. The resulting increased pressure in a pressure chamber flexes a diaphragm along one side of the pressure chamber, to open a main valve.
While these devices perform satisfactorily, they have inherent difficulties as well, including their large size and weight, the required level of volts and watts to operate the pilot valves, their relatively high fabrication cost, and their lack of direct compatibility with digital data storage and handling apparatus. This final disadvantage is substantial in view of the continuing trend to increasingly employ microprocessors in controlling valves and other devices. A further disadvantage is the lack of ability to modulate these pilot valve structures, i.e. to effectively adjust the pilot valve to a position intermediate fully open and fully closed.
Therefore, it is an object of the present invention to provide a fluid valve in which the servo valve is compatible with transistor-transistor logic (TTL), to facilitate microprocessor control including modulation of the pilot valve.
Another object is to provide a fluid valve in which a fixed orifice, a variable servo orifice and a fluid flow sensing device are provided in a monolithic semiconductor chip.
A further object of the invention is to provide a gas valve in which a normally open servo valve maintains the main valve closed while providing an acceptably low flow of gas.
Yet another object is to provide a low cost and reliable fluid valve operable at low voltages.